Explosion turbine



PatentedDec. '4, 1934 PATE-N1' OFFICE 1,932,665 A l EXPLOSION TURBINEHans Holzwarth, Dusseldorf, Germany, 'assigner' to Holzwarth Gas TurbineCo San Francisco,

Calif., a corporation ofDelawar ApplioationApril 19, 1929,`l Serial No.356,446

In Germany April 30, 1928 4 Claims.o (Cl. 6041)` sideration.As'alreadyvstated, however,`th fac- My invention relatesto explosionturbines of theI-Iolzwarth type wherein charges of fuel and.

air are periodically fedito one or more explosion chambers associatedwith the rotor of the turbine to. be exploded in such chambers underconstant volume and then discharged at predetermined instants into anexpansion nozzle which directs the combustion gases against the bladesof the rotor, each explosion and expansion being'followed by alscavenging period during which the residual explosion gases are drivenout of the explosion chamber through the same expansion nozzle; and moreparticularly to the constructional relationship of certain parts of suchturbine wherebya stable and eiicient operation of a plant of this typefor indenite periods is obtained.

My present invention has for its primary object the construction of anexplosion turbine,- of the type referred to, which will be stable inoperation,

that is, will operate yfor an indenitetime without difiiculty orstoppagefrom premature ignition.

It has for its secondary object the constructionl of such 'a turbinewhich will be not only stable but as efficient as otherwise possible; It4is obvious that, whatever may be'the degree `of efliciency of such anengine, any substantial lack of stability will be fatal to its operationas a whole,-

1 and that therefore its construction, must be de# signed first forstability and only secondarily rfor an efficiency as high as possibleunder the cir-'f cumstances. While, therefore, in carrying out my Ainvention, other things being equal, considerations of stability mustdominate any relevant constructional detail of the engine, even at thecost of maximum possible eiiiciency, it is in some cases possible thatsuch a maximum eii'iciency mayr nevertheless beobtained. I have foundthat the relative size of -the smallest cross-section of the nozzlethrough -which the residual gases escape as they are expelled from vthecombustion chamber is an important element of such an engine and largelydetermines its stability of operation, and as I' have already pointedout heretofore in my pending application Serial No. 186,094, therelative size of the smallest cross-:section of the nozzle through whichthe gases expand is an important element in operating such an engineefficiently. Asmy invention relates to an engine inwhich bothv theexpanding gases and the scavenged gases escape through the samenozzle itis obviousJ that there is a close inter-relation between the i'actorsgoverning stabilityand' the factors governing eiliciency, and that' forthe proper designing of a commercial engine of this typeboth sets oifactors must be taken into contors making for stable operation'must inany highest possi/ble eiliciency can be permitted to prevail only-in sofar as they do notinterfere with the former set of factors.' l

As it is usually the primary endeavor of lthe mechanical. engineer sotodesign an engine as to obtain the highest possible efciency I will rstgive a brief description of the features which should be givenconsideration when designing an'engine of this type from the standpointof highest efiici-I ency, that is, other things being equal, from thestandpoint of the avoidancev -as far as possible of heat losses duringthe expansion of the gases.

It is believed also that in'this way the problemA which remained evenafter I.had discovered the principles'y of construction forobtalning'highest eflciency will be better understood; it is the primaryobject of my invention to solve this problem.

to the whirling of the gases in the nozzle chamber connecting the outletend of the explosion chamber with the nozzle, can-be very' greatlyreduced by observing lthe following constructional formula i V l wheref. the smallest nozzle cross-section measured in square centimeters andV=the volume .of the combustion chamber measured- -in cubic meters, itbeing assumed' that the nozzle. valve is as large as practicable andisopened as quickly as possible.V

As explained in the above cited application, a nozzle dimensioned inaccordance with this formula has a' minimum crosssection which isconsiderably below that recommendedL by the prior art, and in fact suchconstructional relationship is quiteV contraryto the teaching of theprior 'art whichcalled for a nozzle opening as Alarge as practicable topermit rapid discharge of the gases.

The above constructionalv relationship is the result of my discoverythat itis more important to prevent whirling `in the vnozzle channelthan to discharge thegases in a ottime l! excessive heat losses Jin suchYchannel are to. be avoided;

.residual gases in each and that the prevention of such whirling iseiected by reducing the minimum nozzle crosssection to such an extentthat upon opening of the nozzle valve (which, as is known, should beopened tained, I make the nozzle channel leading to the nozzle as smallas possible, and in a further development of the idea, I have departedfromthe teaching of the explosion turbine artand also from the steamturbine art by employing, for each combustion chamber, a singledischarge nozzle having a single unobstructed outlet, as disclosed in mycopending application Serial No. 186,095, filed April 23, 1927. In thisway, for a given total eiective area of nozzle outlet, I obtaina nozzlehaving a much smaller circumferential length than, for instance, anozzle whose outlet is divided into a number of passageways by vanes orblades but has the same given total eifectivearea. I am thus enabled toconstruct the nozzle channel between the nozzle valve and the point ofminimum cross-section of the nozzle as small as possible, so that theadvantages in heat economy obtained by constructing the turbine inaccordance with the formula f -17-40 to 100 may be more completelyrealized, as with al smaller nozzle channel the pressure is more rapidlybuilt up therein and made equal to that prevailing 4.in thev explosionchamber upon opening of the l nozzle valve. y

I have observed in the operation of a number of explosion turbines builtby me in accordance with the rules and formulas available' in this art,even those built in accordance with the formula hereinabove explained,that after the turbine has been running for a short time, pre-ignitionsets in.

whereupon the operation of the turbine becomes unstable and nallyceases. This condition pointed to the fact that a very hightemperature,suillcient to ignite an incoming charge, had been reached in theexplosion chamber. Both prac.- tice and theory have demonstrated thatthis rise' in temperature cannot ordinarily be prevented by Dumping moreor cooler cooling medium through --the cooling Jackets with which thevexplosion chambers are usually provided. ""'I'he present invention aimspre-ignition and to provide anexplo'sion-turbine to `prevent such whichis stable in operation and at the same time 'suffers a minimum of heatlosses, so that the etliciency thereof is maintained at a high level.

I have determined that this pre-ignition is due to incomplete scavengingof the combustion chamber of the residual combustion gases, suchresidual gases progressively raising the explosion temperature untilthey are suillciently hot to ignite the incoming charge eve'n thoughadmixed 4with a large proportion of scavenging air. That the presence oflcomparatively small amounts of successive fuel and air charge in theexplosion chamber could so detrimentally aiiectthe operation oftheturbine was hardly to be'expected, as explosion engines ingeneral-are known tooperatesatisiactorily with 'in my United States myinvention by observing a certain minimumrelationship discovered by me,and capable of being expressed mathematically, between 'certain elementsof the explosion turbine and the time allotted to the scavenging portionof the explosion cycle of the combustion chambers. I have found that theduration of the scavenging period is of the highest importance and thatthe same is organically linked up with the Vdimensions of certainelements of the explosion turbine, and that this minimum relationshipImust be adhered to before a turbine stable in operation can beconstructed. That this relationship existed was never before known, norcan the mathematical expression thereof be deduced from the hithertoAknown relationships between the parts of an explosion turbine. VThisnew relationship discovered by me must moreover be observed beforeadvantage can be taken of-the optimum relationship exhaust pressuresandthe dimensions of the' nozzle.

Fig. 1 Ashows an explosion chamber a of substantially cylindrical formwhich is periodically charged withI a mixture of air and fuel .throughthe valvesb and c, the mixture being exploded 4therein at predeterminedinstants by means of a spark plug or other ignition element After theexplosion a nozzle valve d is, opened and thel combustion gases arepermitted to escape into the nozzle channel e which directs them into anexe pansion nozzle 'a and they are then ldischarged 4against the bladesh of the turbine rotor. It will be understood that the valves c, b, andd are timed and controlled in any suitable manner, as for instance by acontrolling mechanism in the form of a pressure oil distributor m shownmore in de-.

' tail in my'Patent No. 877,194.

After^the explosion and discharge lof the gases from the combustionchamber the latter is scavenged of the residual combustion gases. .This

scavenging may be eiIected by means of a stream of scavenging aircharged by a separate scavenging valve (not shown), butI prefer toeiiect such scavenging by meansot the air designed to support thecombustion-o! the fuel. To this end, the

combustion chamber a is made of elongated form, as illustrated, and thenozzle valve d kept open during the initial charging period for thecombustion air. Due to the elongated formof the chamber this combustionair pushes' the residual combustion gases before it in the manner of a.piston. The nozzle valve is so timed that it is closed at the momentthat the advance portion of such air reaches the outlet end o! thecombustionchamber. The piston eiIect may be increased by making theinlet end of the explosion -chamber conical ,as shown in my copendingapplication Ser` No. 376,135, tiled July 5. 1929 and Letters Patent No.1,810,768. By so employing the charging air to effect 1,982,665'scavenging ofthe chambeni reduce the time for a complete explosion cycleby the time required to charge a separate stream of scavenging air.

- In the design of an explosion turbine which is -to have agivencapacity itis` necessary first to determine the number of explosioncycles that 4are to take place in each combustion chamber per minute. Itis, of course, generally desirable tohave as many explosions per minuteas pos-- sible in o'rder to increase 'the capacity of `the machine andthus increase the power output per ton of weight.

In, addition to the number of cycles tobe eml ployed per minute, it isnecessary to determine l5 also the size of the combustion chamber, thesize of the nozzle valve, the minimum cross-sectional area of thenozzle,l and the various pressure relations to be employed. Theconsiderations involved in the dimensioning 'of these several elementsare'not simple and are. not of a Y purely mathematical nature. Theseconsideranozzle.

gases referred to under 9.

5. The form or shape of the combustion chamber, its ratio of length todiameter, andthe appendages upon its inlet and outlet ends.

6. The degreeof whirling of the residual combustion'gas'es with theincoming charge of scavenging' air.

7. Tl'le extent of heat exchange between the combustion gases and thewallsof the combustion chamber, the nozzle channel and the nozzle.

3. The temperature of the combustion gases.

9. The permissible amount of residual combustion gases in the'newexplosive charge.

0f the above, only the factors 1, 2 and 3 can in general be determinedmathematically from known data. With respect to the factor 5, certainrules of construction for explosion chambers be applied upon whichfactors Sand 'l are in part dependent. The number, size and form of thecombustion chamber will in part depend upon the capacity of the turbine,which in a measure controls also the temperature of the combustion gasesindicated under 8, and will depend in part also on the `nature of thefuel employed, which in turn bears a relation also to the permissible'amount of residual combustion My researchesihave indicated that the sizeof the minimum cross-section of the nozzle, listed under 4, is-of verygreat importance. As above indicated, by reducing this minimum nozzlecrosssection below the size heretofore employed in this art, I reducethe amount of heat lost in the nozzle channel due to whirling, andthough I 'increase theloss dependent on the time factor, yet theresultant is an enormous increase in heat econ.-` omy. On the other handI have found that pre-f ignition is caused by the presence of residuacombustion gases in the new charges fed to the vexplosion chambers, andthat it is necessary to insure as complete scavenging as possible. Thecompleteness of the scavenging will depend, at least in part, upon thetime allowed for the same 'and' upon the size of the minimumcross-section attainedI has been 4by reducingv the. scavenging period'by making the minimum nozzle `cross.

.sectionj relatively large to permit discharge of theresidual gaseswithin va minimum, of time.

vThis reduction inI scavenging timeand increase in nozzle cross-sectionI havefound to have more or less criticalv limits from the standpointboth l of stable operation and of eiciency, first' because of mydiscovery that it is incomplete scavenging that' is responsible for thegradual building up of thetemperature within thel combustion chamberwhich ultimately.l causes pre-ignition, and

that therefore suliicient time must be allowed to permit substantiallyall of the residual combustion gases to escape from the combustionchamber; and secondly, because as the minimum nozzle cross-section isincreased,`the volume of the 'nozzle channel is likewise increased sothat, as explained above in connection with my copending applicationSerial No. 186,094, the heat losses due to whirling in such channel areenormously in creased. Different considerations thus require differentsizes of minimum nozzle cross-section and different scavenging periods.mined, as indicated below, that a definite rela- -tion exists betweenthe scavenging period, the

size of the explosion chamber, and the minimum nozzle cross-section,which relation, defines the conditions for both stable and eilicientexplosion the drawing is indicated as taking place at the point 1 andconsumes the time 1-1; secondly,

I have deterthe so-called saddlel from the instant l' to the instant 2,during which the nozzle valve is kept closed to insure completecombustion of the exploded charge, the valve being quickly opened anddepends primarily upon the thermal content of the explosive mixture. Ihave found that optimum conditions are maintained when a mixture havinga heat content of 400 to 450 kg. cal..p=.`

according to the example taken, 0.06 second for.

the explosion, 0.01 second for the saddle and 0.13 second for thecharging. There thus remains v0.8 second for the expansion of theexploded gases and the scavenging of the residual gases remaining in thecombustion chamber. The present invention is concerned primarily withthe splitting or apportioning of this residual period of the explosioncycle in such manner that a stable operation of the turbine is assuredwhile at the same time a high efficiency is obtained. y

The scavenging'period 3-4 is indicated as Z in Fig. 2. The

period with the ratio Pa until, upon reaching-the critical pressurerelationship, such amount attains its highest value. the case of auniformly cylindrical nozzle this critical pressure relationship isexpressed by the the expansion ratio of the nozzle, F=the outlet area ofthe nozzle, and f=the minimum crosssection of -the nozzle (Fig. 3).

The graph of this formula is shown in Fig. 4

where the relationship between the values and p (the latter based on theassumption of an exhaust pressure p0=1.06) on one hand and on the`other, is indicated. It is clear from the graph that the greater theexpansion ratio of the nozzle thesmaller is the pressure ratio andconsequently the smaller is the necessary scavenging air pressure, andthe more rapidly will the chamber therefor be freed of residual comybustion gases.

The value yfor cannot be arbitrarily xed. In the first place itdetermines in large measure the velocity at'which the gases strike theturbine blades, and thus affects the' speed of the turbine; itdetermines also the dimensionsof the turbine rotor and the efiiamount ofgasescaping from theA chamber a per unit of time rises during this"cated above.

ciency of the energy transference. from the gases to the rotor. On theother hand, the ratio determines the scavenging pressure to the extent*vthat the.latter must not be below the pressure pL derived from the aboveformula, or. from the graph of Fig. 4, if an unnecessarily prolongedscavenging period, and hence arreduced number of cycles and increasedloss of heat, or else an incomplete scavenging of the explosion chamberandthe consequent danger of pre-ignition,v are to beavoided. In this waythe magnitude of a .90 number of the factors bearing on the operation ofan explosion turbine may becalculated.

In accordance with my invention, the nozzle valve is held open duringthe charging of the air which effects scavenging of the explosionchamber for a period of time which is sufficiently long to insure properscavenging. I have found that the duration of this period can beexpressed in terms of the size of the explosion chamber and of thenozzle and that a distinct relationship exists between the minimum timewhich must be allowed for scavenging to insure substantially completeexpulsion of `the residual gases inthe explosion chamber'and avoidanceof pre-ignition,`

and the ratio where f and V represent the-magnitudes indi 110 Thisrelationship is of paramount importance and must be observed if a stableturbine operation is tobe assured, and may be expressed as follows:

Z being the scavenging time in seconds (Fig. 2). This equation expressesmathematically the relation between the nozzle and the combustionchamber to insure substantially complete scavenging and avoidance ofpre-ignition. As the other time divisions of the explosion cycle may becomputed mathematically or fixed arbitrarily,

the relation between the scavenging time, the 105 chamber volume, andthe minimum nozzle crosssection in effect states the interdependence ofthe same with the cycle or explosion frequency of the engine.Pre-ignition can be avoided on operation Y at the highest possiblenumber of cycles only by 1n() operating with a scavenging air pressurewhich is not below the minimum determined by the nozzle ratio and byallowing for the scavenging a time interval which is not below aboutReferring now to the example given above,

wherein it was assumed that each chamber was to be operated at 60 cyclesper minute and where- 140 in it was found that 0.8 second was left forboth vthe expansion and scavenging periods, the values and Z may bedetermined as follows: It is known that be observed:

=f(T).* For best efficiency the following equationmust Assuming f n,,100 A and substituting in the scavenging equation fz; 4o,

I obtain Z=0.4 sec.

The value of T can be obtained from Equation If this should be greaterthanOA sec., so that Z-l-T 0.8, then the number of cycles per minutemust be reduced, or else must be made greater than 100 and the heateconomy of the turbine-sacriced. If T is less than 0.4 sec., say 0.2sec., then either a lower value for may be selected, with consequentincrease in heat economy in the nozzle channel, or the number of cyclesper minute may be increased, so that greatl er capacity per unit ofmachine weight may be obtained. In this way the expansion and scavengingperiods are determined and also the. ratio V 'Ihe actual value of ,f andV will' obviously depend upon the size ofthe machine andthe numberlequal to about 3.5 f gives very satisfactory results;

while with suitable mechanism the opening period may be reduced to 0.006sec., whereby the whirling period in the nozzle channel is greatlyreduced and the heat losses in such channel limited to about 10%. 1 l

As already indicated hereinabove, stability is a matter ofj primaryimportance to `which any conflicting considerations of eiicienc'y mustyield,

asY a stable engine of a comparatively lower degree of eiciency is farpreferable from a commercial standpoint to an unstable engine of highereiciency. It is therefore obvious that in the construction of my engine,wherein the volume of the combustion chamber is V and the time allowedfor scavenging Z, the smallest nozzle'cross-section 1 10000 y ,)Rf 1*]VT rem/s+ 273 p, where p2 pressurev in ats. at point 2 of Fig.

2 temperature in C. at point 2 of 2. p3 pressure in ats. at point 3 ofFig. l

(f) must be of a size substantially corresponding tothe formulaV .VZ-40. y l

As alreadyexplainedJ is'not an absolute size but is the `minimum size ofthe smallest nozzle crosssection, and after this minimum has once beenestablished it is obvious that4 from the standpoint of complete andeillcient scavenging this crosssection may be increased if necessary. Ifnow the eiliciency formula f I--40 to 100,

which calls for an optimum or maximum value for the smallest nozzlecross-section, calls in any particular instance for such across-sectionlarger than that called for by the scavenging formula, suchcross-section should be, chosen as 'is called for by the efiiciencyvformula. If, on .the other hand, the eiciency formula calls for a.smaller cross-section than that called for by the scavenging formula,the result of the scavenging formula must control.

I claim:

1. In combination, an explosion chamber, air and fuel charging valves atthe inlet end of said chamber, an outlet valve at the outlet end of saidchamben a discharge element, a channel between,

said discharge element and the outlet .end of said chamber, means forexploding a combustible mixture fed by said charging valves, said outletvalve being adapted to be opened a definite time after I said explosionto "discharge the`v combustion gases into said discharge element, saidair valve being adapted to be opened when the pressure in said chamberis a definite amount vabove the counter pressure beyond said dischargeelement, means for holding said outlet valve open for a' periodsufficient to insure'substantially complete scavenging of said chamberof the residual combustion gases, and means for closing said valve atthe end of such period, said period, measured in seconds, beingsubstantially 40 times the ratio of the volume of the explosion chamber,measured in cubic meters, to the minimum cross-sectional area of the'discharge element, centimeters.

2. In combination, an explosion chamber, air and fuel charging valves atchamber, an outlet valve at the outlet end 4of said chamber, a dischargeelement, a channel between said discharge elementand the outlet end ofsaid chamber, means for exploding a combustible mixture fed by saidcharging valves, saidoutlet valve being adapted to be opened a definitetime after said explosion to discharge the combustion gases into saidelement, saidy air valve being adapted to be opened when the pressure insaid chamber is a definite amount above the counter-pressure beyond saiddischarge element to charger air into such chamber at` a pressure abovethe critical pressure, means for holding said outlet valve open fora/'period suilicient to insure .substantially complete scavenging ofysaid chamber of the residual combustion gases, and means for closingsaid valve at the end of such period, said period, measured in seconds,being at least 40 times the ratio of the volume of the explosionchamber, measured in cubic meters, to the minimum cross-'sectionalareaof the discharge element, measured theinlet end 'of saidmeasured insquare explosion engine which comprises charging air and {uel into anexplosion chamber forming part of such engine, exploding said airandfuel, dis-v v charging the resulting combustion gases from saidchamber into a discharge element, and charging and fuel into anexplosion chamber forming part of such turbine, exploding said air andfuel, discharging the resulting combustion gases from said chambeigintoa. discharge element, and charging scavenging air into said chamber at apressure above the critical pressure to drive out the resid- Kualcombustion gases, said scavenging air being charged for a suiicientlylong period to insure substantially complete scavenging of said chamber,said period measured in seconds being at least about-40 times the ratioof the volume of the explosion chamber, measured in cubic meters, to theminimum cross-sectional area of the discharge element, measured insquare centimeters, said ratio being as closely as possible within thelimits 1/100 to 1/40. Y

HANS HOLZWARTH.

